The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
Design of high quality biomedical devices to gather real-time physiologic parameters from a patient body could be the key point in saving the patient's life. These devices monitor biomedical signals in order of volts, V, to mV at the body surface and hence are susceptible to noise and interference. Low power, highly linear analog filters have wide range of applications in biomedical signal processing for example, a hearing aid as described in I. Deligoz, S. R. Naqvi, T. Copani, S. Kiaei, B. Bakkaloglu, S. Je, and J. Chae, (“A MEMS-based power-scalable hearing aid analog front end,” IEEE Tran. on Biomed. Circ. and Syst., vol. 5, no. 3, pp. 201-213, June 2011—incorporated herein by reference), photoplethysmogram as described in A. Wong, K. Pun, Y. Zhang, and K. Nang Leung, (“A low-power CMOS front-end for photoplethysmographic signal acquisition with robust DC photocurrent rejection,” IEEE Tran. on Biomed. Circ. and Syst., vol. 2, no. 4, pp. 280-288, December 2008—incorporated herein by reference), electrocardiogram (ECG) as described in S. Lee, and C. Cheng, “Systematic design and modeling of a OTA-C filter for portable ECG detection,” IEEE Tran. on Biomed. Circ. and Syst., vol. 3, no. 1, pp. 53-64, February 2009—incorporated herein by reference), wearable breathing detector as described in P. Corbishley and E. Rodriguez-Villegas, (“A nanopower bandpass filter for detection of an acoustic signal in a wearable breathing detector.” IEEE Tran. on Biomed. Circ. and Syst., vol. 1, no. 3, pp. 163-171, 2007—incorporated herein by reference), pulse oximeter as described in K. Li and S. Warren, “A wireless reflectance pulse oximeter with digital baseline control for unfiltered photoplethysmograms,” IEEE Tran. on Biomed. Circ. and Syst., vol. 6, no. 3, pp. 269-278, June 2012—incorporated herein by reference), acquisition of various neurophysiological signals as described in M. Mollazadeh, K. Murari, G. Cauwenberghs, and N. Thakor, (“Micropower CMOS integrated low-noise amplification, filtering, and digitization of multimodal neuropotentials,” IEEE Tran. on Biomed. Circ. and Syst., vol. 3, no. 1, pp. 1-10, February 2009—incorporated herein by reference) and M. Mollazadeh, K. Murari, G. Cauwenberghs, and N. Thakor, “Wireless micropower instrumentation for multimodal acquisition of electrical and chemical neural activity,” IEEE Tran. on Biomed. Circ. and Syst., vol. 3, no. 6, pp. 388-397, December 2009—incorporated herein by reference), neural spike detection as described in A. Rodríguez-Pérez, J. Ruiz-Amaya, M. Delgado-Restituto, and Á. Rodríguez-Vázquez, “A low-power programmable neural spike detection channel with embedded calibration and data compression,” IEEE Tran. on Biomed. Circ. and Syst., vol. 6, no. 2, pp. 87-100, April 2012—incorporated herein by reference), EEG monitoring as described in R. F. Yazicioglu, P. Merken, R. Puers, and C. V. Hoof, (“A 200 uW eight-channel EEG acquisition ASIC for ambulatory EEG systems,” IEEE J. Solid-State Circuits, vol. 43, no. 12, pp. 3025-3038, December 2008—incorporated herein by reference), and neural recording systems as described in A. Wong, K. Pun, Y. T. Zhang, and K. Hung, (“A near-infrared heart rate measurement IC with very low cutoff frequency using current steering technique,” IEEE Trans. Circuits Syst. I, vol. 52, no. 12, pp. 2642-2647, December 2005-incorporated herein by reference).
However, as recognized by the present inventor, designing ultra-low frequency filters for biomedical signal processing is a challenging problem due to the difficulty in developing efficient methods achieving large time constant while maintaining high linearity performance.